NEW YORK — Wal-Mart stock had its biggest one-day drop in nearly three decades after the world’s largest retailer said it’s bracing for its profit to take a hit as it works to fend off competition.

The company is forecasting its profit to fall by as much as 12 percent in its next fiscal year as it perks up customer service and adapts to changing shopping habits. It also expects sales for this full fiscal year to be flat, hurt by unfavorable currency exchange rates. Wal-Mart had previously forecast sales growth of 1 to 2 percent.

Its stock closed down $6.70, or 10 percent, at $60.03 Wednesday.

The disappointing guidance comes as Wal-Mart Stores Inc. works to fix its business amid pressure from rivals including traditional grocers, dollar stores and Amazon.com. At its annual meeting in New York City Wednesday, CEO Doug McMillon sought to reassure investors that that the profit decline next year is part of its plans to position for the future.

“We all know that retail has changed and will continue to change at an accelerating pace,” said McMillon, who took the job in February 2014.

Under McMillon, Wal-Mart has accelerated the openings of smaller stores, which tend to be more conveniently located and let customers get in and out faster. On Wednesday, it also said it was expanding its online grocery with free pickup to 10 additional markets, making the service available in a total of 20 markets in the U.S.

Such moves, along with a push to improve the cleanliness of its U.S. stores, are expected to help attract more higher-income customers than in the past, McMillon said. But he noted the company would also remain focused on shoppers who are driven by low prices.